Chimaeric human papillomavirus 16 L1 virus-like particles and a method for preparing the particles

ABSTRACT

A method for producing a chimaeric human papillomavirus (HPV) L1 polypeptide containing a heterologous peptide, and in particular, a HPV L2 peptide comprising the steps of introducing a DNA sequence coding for the heterologous peptide into a DNA sequence coding for the L1 polypeptide; introducing the DNA sequence including the sequences for the L1 polypeptide and heterologous peptide into a host cell in which the DNA sequence can be expressed; causing expression of the DNA sequence; and recovering the resulting chimaeric L1 polypeptide which includes the heterologous peptide. The invention also describes a vector for use in the method, a host cell containing the vector, and a vaccine including the chimaeric HPV L1 polypeptide produced according to the method.

BACKGROUND OF THE INVENTION

The invention relates to a method for preparing polypeptides, and in particular virus-like particles (VLPs) or capsomers of human papillomavirus.

The papillomaviruses are a group of small DNA viruses, which induce warts and other lesions in a variety of higher vertebrates including humans.

Papillomaviruses (PV) are members of the genus Papillomavirus, family Papillomaviridae, and contain a double stranded circular DNA genome with a typical size of 7 900 base pairs (Seedorf et al., 1985). All PVs have a similar genomic organisation, with an early gene region encoding proteins involved in DNA replication and cellular transformation, and a late region encoding the viral capsid proteins (FIG. 1). A non-coding region known as the long control region (LCR) contains control elements for transcription and replication.

Papillomaviruses encode two viral structural proteins, L1 and L2. The virion contains 360 L1 molecules arranged as 72 capsomers, each of which is a pentamer composed of five L1 molecules (Baker et al., 1991). The ratio of L1 to L2 molecules has been estimated as approximately 30:1 (Doobar et al., 1987), which suggests that each virion would contain approximately twelve L2 molecules. The greater number of L1 molecules per virion has led to L1 being referred to as the ‘major’ capsid protein and L2 being referred to as the ‘minor’ capsid protein.

HPV-16 L1 is encoded by a 1.518 kb gene, giving rise to a protein of 504 amino acids. L1 has a molecular weight of 55 to 58 kD (Browne et al., 1988). Domains of L1 are likely to mediate cell binding and to contain antigenic determinants mediating antibody and T cell immune responses to the virus.

Among the genital human papillomaviruses (HPVs), there are low risk HPVs (for example, HPV 6 and HPV 11) that cause genital warts and cervical lesions that usually regress or do not progress to malignancy, and high risk (or oncogenic) genotypes (for example, HPV 16 and HPV 18), which are associated with high-grade cervical lesions and carcinomas. HPVs have also been implicated as the etiological agents in several other anogenital and upper aerodigestive tract cancers (Breitburd et al., 1999). A compelling body of clinical, molecular, experimental and epidemiological evidence has established that certain HPV types are the main cause of cervical cancer (Lowy et al., 1994; IARC, 1995).

HPV 16 is present in most cases of cervical cancer cases and an additional three types (HPV 18, 31 and 45) are present in approximately an additional 30% of cases (IARC, 1999).

Although the incidence of cervical cancer is decreasing in the US, it is the most common malignancy in women in developing countries, with about 500 000 new cases diagnosed each year.

Traditionally most prophylactic vaccines have consisted of live, attenuated virus or formalin inactivated virus. Papillomavirus virions are highly immunogenic, inducing high titres (>10 000) of neutralising antibodies when systemically inoculated (Doretzky et al., 1980; Kirnbauer et al., 1991, 1992). However, due to the difficulties and risks involved in generating large quantities of these traditional vaccines there has been great emphasis on the development of viral protein subunit or virus-like particle (VLP) vaccines.

The best candidate protein for a prophylactic vaccine against HPV is the major capsid protein L1, which self-assembles into VLPs (Schiller and Lowy, 2001). These VLPs are very well characterised, and morphologically appear indistinguishable from whole virions (Chen et al., 2001; Rose et al., 1993). Injection of VLPs into experimental animals induces neutralising antibodies (Rose et al., 1998); preliminary human trials of injected VLP vaccines have also shown that these are well tolerated and highly immunogenic, and in the former case, stimulated robust B and T cell responses (Evans et al., 2001; Harro et al., 2001).

An effective, cheap prophylactic vaccine against oncogenic types of mucotropic HPVs could potentially have an impact on the world cancer burden, especially against HPV 16.

A common-neutralizing epitope for HPV types 6 and 16 has been found in the region (aa) 108-120 of the HPV 16 minor capsid protein, L2 (Kawana et al., 1998, 1999). Balb/c mice that were nasally immunised with a synthetic peptide corresponding to the epitope elicited an immune response that resulted in IgA and IgG antibodies cross-reacting with L1/L2 capsids of HPV 6, 16 and 18 (Kawana et al., 2001). Immunisation of rabbits with either of two overlapping peptides derived from the L2 sequence region 94-122 from either Rabbit oral papillomavirus (ROPV) or Cottontail rabbit papillomavirus (CRPV) resulted in sera which reacted to purified cognate L2, specifically recognised L2 in infected cells, and neutralised virus in vitro. Rabbits immunised with CRPV peptides were immune to CRPV challenge (Embers et al., 2002).

The inventors therefore decided to further investigate the presentation of this L2 epitope on chimaeric L1 VLPs as a vaccine in its own right, and as a model for the presentation of other immunogenic peptide sequences.

SUMMARY OF THE INVENTION

According to a first embodiment of the invention, there is provided a method for producing a chimaeric human papillomavirus (HPV) L1 polypeptide containing a HPV L2 peptide, the method comprising the steps of:

-   -   introducing a DNA sequence coding for the L2 peptide into a DNA         sequence coding for the L1 polypeptide;     -   introducing the DNA sequence including the sequences for the L1         polypeptide and L2 peptide into a host cell in which the DNA         sequence can be expressed;     -   causing expression of the DNA sequence; and     -   recovering the resulting chimaeric L1 polypeptide which includes         the L2 peptide.

The HPV L1 polypeptide and/or HPV L2 peptide may be a HPV-16 polypeptide or peptide.

The HPV L2 peptide may have the following amino acid sequence: LVEETSFIDAGAP (SEQ ID NO: 1), or a sequence which is modification or derivative thereof, with the proviso that the modified or derived sequence is a sequence which has at least 80% homology to the sequence of SEQ ID NO: 1 and codes for a peptide which elicits an immunogenic response against HPV.

One or more nucleotides of the L1 DNA sequence may be deleted at the point of introduction of the L2 DNA sequence, and typically the number of nucleotides deleted from the L1 sequence will correspond with the number of L2 nucleotides inserted.

The expression of the protein could either be in a prokaryotic or eukaryotic expression system.

The chimaeric polypeptide may have the amino acid sequence set out in any one of FIGS. 6, 8, 10, 12 and 14 (SEQ ID NOs: 5, 7, 9, 11 and 13), or a sequence which is at least 80% homologous to any one of the sequences set out in SEQ ID NOs: 5, 7, 9, 11 and 13 and which is capable of eliciting an immunogenic response against HPV. The DNA sequence coding for the chimaeric polypeptide may be the DNA sequence as set out in any one of FIGS. 5, 7, 9, 11 and 13 (SEQ ID NOs: 4, 6, 8, 10 and 12), or a sequence having at least 80% homology to any one of these sequences and which codes for a polypeptide capable of eliciting an immunogenic response against HPV.

The chimaeric L1 polypeptide may assemble into virus-like particles and/or capsomers. The virus-like particle or capsomer may be immunogenic.

According to a second embodiment of the invention, there is provided a chimaeric HPV L1 DNA sequence into which the DNA sequence coding for the above HPV L2 peptide has been inserted, the resulting HPV L1 sequence being capable of expressing the HPV L2 peptide.

One or more nucleotides of the L1 DNA sequence at the point of introduction of the L2 DNA sequence may be deleted, and typically the number of nucleotides deleted from the L1 sequence will correspond with the number of L2 nucleotides inserted.

The chimaeric nucleic acid sequence may be a sequence as set out in any one of FIGS. 5, 7, 9, 11 and 13, or a DNA sequence which is a modification or derivative thereof, with the proviso that the modified or derived DNA sequence has at least 80% homology to any one of the sequences of SEQ ID NOs: 4, 6, 8, 10 and 12 and codes for a chimaeric L1 peptide which is capable of eliciting an immunogenic response against HPV.

According to a third embodiment of the invention, there is provided a vector including the nucleic acid sequence described above.

According to a fourth embodiment of the invention, there is provided a host cell including the vector described above.

According to yet a further embodiment of the invention, there is provided a chimaeric HPV L1 polypeptide that includes the above HPV L2 peptide (SEQ ID NO: 1).

The chimaeric polypeptide may be a chimaeric HPV L1 virus-like particle or capsomer.

According to a further embodiment of the invention, there is provided an HPV polypeptide having the amino acid sequence set out in any one of FIGS. 6, 8, 10, 12 and 14 (SEQ ID NOs: 5, 7, 9, 11 and 13), or a sequence which is a modification or derivative thereof, the modification or derivative being a sequence which is at least 80% homologous to any one of the sequences set out in SEQ ID NOs: 5, 7, 9, 11 and 13 and which is capable of eliciting an immunogenic response against HPV.

According to another embodiment of the invention, there is provided a method for producing a chimaeric human papillomavirus (HPV) L1 polypeptide containing a heterologous peptide, the method comprising the steps of:

-   -   introducing a DNA sequence coding for the heterologous peptide         into a DNA sequence coding for the L1 polypeptide;     -   introducing the DNA sequence including the sequences for the L1         polypeptide and heterologous peptide into a host cell in which         the DNA sequence can be expressed;     -   causing expression of the DNA sequence; and     -   recovering the resulting chimaeric L1 polypeptide which includes         the heterologous peptide.

The heterologous peptide sequence may be any other HPV sequence, or may be derived from any antigenic epitope, B-cell or T-cell specific.

One or more nucleotides of the L1 DNA sequence at the point of introduction of the heterologous DNA sequence may be deleted, and typically the number of nucleotides deleted from the L1 sequence will correspond with the number of heterologous nucleotides inserted.

According to yet a further embodiment of the invention, there is provided a vaccine including the chimaeric HPV L1 polypeptide or a DNA sequence coding for the polypeptide, substantially as described above. The vaccine may be for prophylactic or therapeutic treatment of HPV infection, in particular HPV 6, 16 and 18.

Preferably, the vaccine will be capable of inducing an immunogenic response to HPV and to the introduced peptide in a suitable host.

The vaccine may further include a pharmaceutical excipient and/or adjuvant.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic representation of the genomic organisation of HPV 16;

FIG. 2 shows the monomer structure of HPV 16 L1;

FIG. 3 shows the nucleotide sequence of the native sequence of the HPV 16 L1 gene into which the L2 epitope was inserted to produce the chimaeric constructs of FIGS. 5 to 14 (SEQ ID NO: 2);

FIG. 4 shows the amino acid sequence of FIG. 3 (SEQ ID NO: 3);

FIG. 5 shows the nucleotide sequence of chimaeric construct A (SEQ ID NO: 4);

FIG. 6 shows the amino acid sequence of chimaeric construct A (SEQ ID NO: 5);

FIG. 7 shows the nucleotide sequence of chimaeric construct C (SEQ ID NO: 6);

FIG. 8 shows the amino acid sequence of chimaeric construct C (SEQ ID NO: 7);

FIG. 9 shows the nucleotide sequence of chimaeric construct E (SEQ ID NO: 8);

FIG. 10 shows the amino acid sequence of chimaeric construct E (SEQ ID NO: 9);

FIG. 11 shows the nucleotide sequence of chimaeric construct F (SEQ ID NO: 10);

FIG. 12 shows the amino acid sequence of chimaeric construct F (SEQ ID NO: 11);

FIG. 13 shows the nucleotide sequence of chimaeric construct H (SEQ ID NO: 12);

FIG. 14 shows the amino acid sequence of chimaeric construct H (SEQ ID NO: 13);

FIG. 15 shows a diagrammatic representation of the chimaeric construct A;

FIG. 16 shows a diagrammatic representation of the chimaeric construct C;

FIG. 17 shows a diagrammatic representation of the chimaeric construct E;

FIG. 18 shows a diagrammatic representation of the chimaeric construct F;

FIG. 19 shows a diagrammatic representation of the chimaeric construct H;

FIG. 20 shows data obtained from end point titrations of mice inoculated with chimaeric VLPs obtained from construct A;

FIG. 21 shows data obtained from end point titrations of mice inoculated with chimaeric VLPs obtained from construct C;

FIG. 22 shows data obtained from end point titrations of mice inoculated with chimaeric VLPs obtained from construct E;

FIG. 23 shows data obtained from end point titrations of mice inoculated with chimaeric VLPs obtained from construct F;

FIG. 24 shows data obtained from end point titrations of mice inoculated with chimaeric VLPs obtained from construct H;

FIG. 25 shows data obtained from end point titrations of mice inoculated with VLPs obtained from a non-chimaeric HPV 16 L1 (SA-opt);

FIG. 26 shows the response of mice to boosters following initial immunisation;

FIG. 27 shows the nucleotide sequence of the L2 peptide which was inserted into the L1 sequence (SEQ ID NO: 14); and

FIG. 28 shows the amino acid sequence of the L2 peptide which was inserted into the L1 sequence (SEQ ID NO: 1).

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Design of Chimaeric Constructs

Primers encoding the peptide:

-   -   LVEETSFIDAGAP (SEQ ID NO: 1)         which is a common-neutralising epitope for HPV 6 and 16 in the         region (aa) 108-120 of the HPV minor capsid protein, L2, were         synthesised.

According to the HPV 16 L1 monomer structure published by Chen et al. (2000) (FIG. 2), various surface loops and regions are exposed when pentamers and high order structures are formed.

Based on the epitope mapping of the V5 antibody (neutralising antibody raised to L1), various regions/loops were selected for the insertion of the L2 peptide so as to maintain the V5 antibody binding region of the L1 VLPs.

The major antigenic region (V5 binding region) of the L1 molecule has been mapped with amino acid residues A266, (with F50 being located beneath the surface residue V271) and S282 (Roden et al., 1996, White et al., 1999). Based on these residues, the inventors decided not to alter the B loop of the molecule, as this would alter the antigenic region and possibly destroy vital L1 epitopes.

The following L1 regions were therefore selected for insertion of the L2 peptide:

-   -   A: E-F loop     -   C: D-E loop     -   E: region between the h4 helix and J region of L1     -   F: h4 helix     -   H: internal C-D loop         Synthesis of Chimaeric Constructs

Chimaeric constructs were prepared by PCR with the primers being designed with the 3′ end coding for the L2 peptide. The HPV 16 SA-opt L1 gene (FIGS. 3 and 4) cloned in the pSK plasmid vector was used as a template. The following DNA sequence was used to encode the L2 peptide:

(SEQ ID NO: 14) 5′-TTAGTGGAAGAAACTAGTTTTATTGATGCTGGTGCACCA-3′.

The L2 peptide was inserted into the gene by replacing the regions shown in Table 1. This method of replacing the existing nucleotides, rather than merely inserting the L2 nucleotides into the L1 sequence without any replacement, is advantageous in that disturbances of the tertiary structure are kept to a minimum, and the possibility of steric effects or interference with antibody binding to nearby sequences due to extra peptide “loops” is minimised.

The position of the inserted L2 epitope is depicted for the chimaeric constructs in FIGS. 15 to 19 respectively.

The chimaeric genes from the sequenced pSK constructs were cloned into a pFastbac1 vector (Sal I/Xba I site). The DNA from the pFastbac1 clones was used to transfect DH10bac cells to prepare bacmid clones.

The chimaeric constructs were expressed in insect cells using the Bac-to-Bac® baculovirus expression system (Life Technologies).

TABLE 1 Insertion of L2 peptide Nucleotide Amino acid position Shown in position Shown in Chimaeric of L2 FIG. No. of L2 FIG. No. construct peptide (SEQ ID NO) peptide (SEQ ID NO) A 520-558 FIG. No. 5 174-186 6 (SEQ ID NO: 4) (SEQ ID NO: 5) C 391-429 FIG. No. 7 131-143 FIG. No. 8 (SEQ ID NO: 6) (SEQ ID NO: 7) E 1291-1329 FIG. No. 9 431-443 FIG. No. 10 (SEQ ID NO: 8) (SEQ ID NO: 9) F 1240-1278 FIG. No. 11 414-426 FIG. No. 12 (SEQ ID NO: 10) (SEQ ID NO: 11) H 241-279 FIG. No. 13 81-93 FIG. No. 14 (SEQ ID NO: 12) (SEQ ID NO: 13)

The bacmid DNA was transferred into sf21 (Spodoptera frugiperda) insect cells using cellfectin. The basic Bac-to-Bac® protocol was followed to amplify the recombinant virus and infect the sf21 insect cells for expression of the chimaeric VLPs.

A basic HPV 16 L1 VLP purification protocol was followed. The infected insect cells were spun down at 3 000 rpm and resuspended in phosphate buffered saline (PBS) with 0.5M NaCl. The suspension was sonicated 4 times at 5 second intervals. This was then overlayed onto a 40% sucrose cushion and pelleted at 100 000×g for 3 hrs. The pellet was resuspended in CsCl buffer (PBS with 0.4 g/ml CsCl) and resuspended by drawing up through 18 and 26 gauge needles to reduce the viscosity before sonication (4 times at 5 second intervals). The suspension was centrifuged at 100 000×g at 10° C. for 24 hrs.

No distinct bands were observed in CsCl gradients. 500 μl fractions were therefore collected and analysed by ELISA using conformation specific V5 and D9 (linear epitope) monoclonal antibodies. Fractions that were found to react to the V5 and/or D9 antibodies were pooled and dialysed against PBS at 4° C. overnight.

Results

Western blots showed that a polyclonal L2 antibody raised to the peptide in rabbits (obtained from Dr. Neil Christensen of The Jake Gittlen Cancer Research Institute, The Milton S. Hershey Medical Centre, Hershey Pa., USA) bound to the chimaeric L1 particles (55 kD), showing that the L2 epitope is expressed by the chimaeric constructs.

Antibody characterisation of the purified VLPs was carried out by ELISA using a panel of antibodies provided by Dr. Neil Christensen (Chistensen et al., 1996, 2001). Table 2 summarises the data.

TABLE 2 V5 E70 U4 9A D9 I23 L2 A + − + + + + + C − − + + + + + E + + + + + + + F + + + + + + + H − − − − + + + SA-opt + + + + − + − L1

A brief description of the antibodies and their binding regions is given in table 3 below.

TABLE 3 V5 Monoclonal, conformation specific antibody; aa 266 and 282 being critical E70 Monoclonal, conformation specific antibody; aa 50, 266 and 282 being critical U4 Monoclonal, conformation specific antibody 9A Monoclonal, binds a linear region in the are aa 1-171 D9 Monoclonal, binds denatured L1 protein I23 Monoclonal, binds in the region aa 111-130 L2 Polyclonal antibody that binding the L2 epitope (aa108-120) Electron Microscopy of the Chimaeric Particles

EM results showed that the particles formed from the chimaeric constructs are not identical to those produced by the wild type HPV L1 gene. The particles formed are mainly in a partially broken down or partially disassembled state and are generally seen to clump together

Animal Experimentation with Chimaeric Antigen

Six sets of 5 Balb/c mice were used for the animal experimentation to determine if inoculation with the chimaeric VLPs elicited an immune response. Chimaeric VLPs produced from the 5 chimaeric constructs and VLPs produced from a non-chimaeric HPV 16 L1 (SA-opt) were injected at a concentration of 100 μg at two sub-cutaneous sites. The animals were inoculated at weeks 0, 2 and 4. Blood samples and vaginal washes were taken at various time periods.

The mouse sera from each group was pooled and analysed by ELISA using VLPs produced in insect cells by recombinant baculoviruses. End point titrations for each group of mice were carried out to determine the extent of the response and give a better reflection of the response (FIGS. 20 to 26).

The results indicate that a high immune response was achieved.

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1. A chimaeric human papillomavirus (HPV) sequence comprising an HPV L1 DNA sequence into which heterologous DNA sequence has been inserted at a region of a L1 polypeptide encoded by the HPV L1 DNA sequence, the region being selected from the group consisting of the E-F loop, the region between the h4 helix and J region of L1, the h4 helix, and the internal C-D loop, wherein the HPV L1 DNA sequence is capable of expressing the heterologous peptide.
 2. The chimaeric HPV sequence according to claim 1, wherein the heterologous DNA sequence is a sequence encoding for a HPV L2 peptide (SEQ I.D. NO: 1).
 3. The chimaeric HPV sequence according to claim 2, wherein one or more nucleotides of the L1 DNA sequence have been deleted at the point of introduction of the L2 DNA sequence.
 4. The chimaeric HPV sequence according to claim 3, wherein the number of nucleotides deleted from the L1 sequence corresponds with the number of L2 nucleotides inserted.
 5. A vector comprising the chimeric HPV sequence as described in claim
 2. 6. An isolated host cell comprising the vector as claimed in claim
 5. 7. The chimaeric HPV sequence according to claim 1, wherein the chimaeric HPV sequence has a DNA sequence set out in any one of SEQ ID NOs: 4, 6, 8, 10 and 12, or a DNA sequence which is a modification or derivative thereof, with the proviso that the modified or derived DNA sequence has at least 80% sequence identity to the insert region of any one of SEQ ID NOs: 4, 6, 8, 10 and 12 and encodes for a peptide being capable of eliciting an immunogenic response against HPV.
 8. The chimaeric HPV DNA sequence according to claim 1, wherein the heterologous DNA sequence encodes a peptide having the amino acid sequence: LVEETSFIDAGAP (SEQ ID NO:1).
 9. A vector comprising the chimeric HPV sequence as described in claim
 1. 10. An isolated host cell compromising the vector as claimed in claim
 9. 